Sinter products for nitrating steel



US. 'Cl. 75-205 13 Claims ABSTRACT OF THE DISCLOSURE Sinter products useful for nitrating steel, and containing nitrogen and one or more steel refining agents, e.g. metals or ferro alloys, have their available nitrogen increased if the mixture of powdered calcium carbide and other starting materials is heated internally at localized heating points, e.g. by electrical resistance heating or thermal reaction process.

This invention relates to a method of producing a sinter product having a high nitrogen content together with steel refining substances, particularly ferro alloys.

For nitrating steels, particularly structural steels, with lime-nitrogen (calcium cyanamide), the nitrogen content of the nitrated steel is relatively poor. It has already been proposed to use a sinter product containing nitrogen and steel refining substances, notably ferro-alloys. A particular advantage for using such sinter alloys is that concurrently with the process of nitration refining substances are introduced into the steel, and also that the use of particulate sinter enables them to be used without causing discomfort to the foundrymen by the generation of dust. Furthermore the high specific gravity of the sinter assures better penetration into the steel melt resulting in a more homogeneous distribution of the nitrogen.

The production of a previously known process for such sinter products included heating an initial mixture of calcium carbide and steel refining substances by the external application of heat, and exposing the mixture to a nitrogen atmosphere. This process may be performed for example by filling reaction vessels e.g. shallow baths or tubes, and placing the filled reaction vessels on or into powdered calcium carbide used for the production of lime-nitrogen. The heat of reaction generated by the calcum carbide surrounding the baths or tubes during the formation of lime-nitrogen heats the mixture contained inside the baths of tubes from the outside. However, such a method permits only small quantities of sinter to be produced, because the heat applied externally is insuflicient to sustain a uniform reaction throughout a large volume of material in the bath or in tubes for example of a diameter exceeding 50 cms. When tubes are used their subsequent removal from the lime-nitrogen block presents difiiculties since the lime-nitrogen that forms around the tubes sinters together considerably.

It has now been discovered that sinter products may be obtained having a high nitrogen content, together with steel refining substances, and which provide an available nitrogen yield of from two to three times that obtained with sinters as herein-before described.

The invention consists of a method of producing a sinter product having a high nitrogen content together with one or more steel refining agents, in which a homogeneous reaction mixture of finely powdered calcium carbide and crushed steel refining agents is raised to reaction temperature by local heating at points in the inter- -nited States Patent Cir ior of the mixture while the mixture is under a nitrogen atmosphere.

The starting materials are homogenised by thorough mixing using for instance bladed mixers, rotary drum mixers, gravity mixers and screw mixers, and then filled into reaction vessels and points in the interior of the mixture raised to reaction temperature. Preferably the local points in the interior of the mixture are distributed to provide from 3 to 5 points per square metre of cross section of the charge.

The reaction temperature of for example 1100 to 1300 C., may be attained by ignition at localized points within the reaction mixture of an igniting mixture or by electrical resistance heating. As igniting mixtures, mixture of alkaline-earth carbides and oxygen-supplying substances have proven to be particularly suitable. Preferably mixtures of calcium carbide and calcium nitrate are used.

The charge of starting materials preferably consists of mixtures of 10 to 50 percent by weight, praticularly 30 to 40 percent by weight, of steel refining agents, the remainder being commercial calcium carbide containing at least 65% and preferably 72 to 74%, of calcium carbide.

The grain size of the calcium carbide used is preferably below 0.5 mm., particularly below 0.1 mm. The grain size of the steel refining agents is preferably likewise below 0.5 mm., particularly below 0.24 mm.

The steel refining agents may be metals, or particularly ferro-alloys such as for example ferro-manganese and ferro-chromium (types affine, surafiine and carb-ure), or ferro-vanadium, ferro-niobiurn-tantalum, ferro-manganese-vanadium, ferro-titanium, ferro-nickel.

The method of the invention may be performed either batch-wise or continuously, in suitable reaction vessels, such as for example cementation furnaces and tunnel furnaces, if the process is performed in a tunnel furnace, the mixture is loaded on mobile reaction trucks, ignited and conveyed through the tunnel furnace under a nitrogen atmosphere. Individual trucks carrying only calicum carbide may be sent through the tunnel furnace between the trucks charged with the reaction mixture.

The following example of the invention is provided:

1520 kg. of a commercial calcium carbide having a grain size below 0.1 mm. were homogenised in a twin shaft mixer, under a nitrogen atmosphere, with 650 kg. of a commercial form-manganese (76% Mn) having a grain size of less than 0.3 mm. The mixture was loosely charged into a Polzeniusz-Krauss open top reaction truck with a box frame fitting conventionally used for the production of lime-nitrogen. The box frame was 1.2 metres high and had an average cross section of about 1.2 sq. m. Five igniting points were prepared from the top, evenly distributed over the cross section, for the reception of an igniting mixture consisting of a commercial calcium carbide and calcium nitrate in a 1:1 proportion by weight, and introduced in quantities of 2 to 3 kg. per igniting point. After ignition the truck was continuously passed through a tunnel furnace in which a nitrogen pressure of 200 mm. water column, was maintained.

The trucks traversed the furnace in the course of several days at the end of which a solid sintered block Weighing 2515 kg. was obtained. This was coarsely crushed. The average nitrogen content was 17.8% and the manganese content 19.6%.

What is claimed is:

1. In a method of producing a sinter product having a high nitrogen content together with one or more steel refining agents, the steps of forming a homogeneous reaction mixture of finely powdered calcium carbide, and one or more crushed steel refining agents, then heating the said mixture to reaction temperature by local heating at a plurality of spaced points in the interior of the mixture while the mixture is under a nitrogen atmosphere, whereby a sinter product is obtained.

2. A method according to claim 1 in which the reaction mixture is raised to reaction temperature at from 3 to 5 localized heating points per square metre of cross section.

3. A method according to claim 1, in which the reac tion temperature is attained by ignition with an igniting mixture at the said localized heating points.

4. A method according to claim 1, in which the reaction temperature is attained by ignition with the aid of electrical resistance heating at the said localized heating points.

5. A method according to claim 1, in which the said homogeneous reaction mixture is a reaction mixture of a calcium carbide and one or more steel refining agents.

6. A method according to claim 5, in which the said homogeneous reaction mixture containing at least 65 wt. percent of a commercial calcium carbide.

7. A method according to claim 6, in which the said homogeneous reaction mixture contains between 72 to 74 wt. percent of calcium carbide.

8. A method according to claim 5, in which the said homogeneous reaction mixture contains between and 50 wt. percent of the one or more steel refining agents.

9. A method according to claim 8, in which the said homogeneous reaction mixture contains between 30 and 40 wt. percent of one or more steel refining agents.

References Cited UNITED STATES PATENTS 3,149,962 9/1964 Mennenoh -27 XR 3,182,102 5/1965 Simnad 75226 XR 3,337,336 8/1967 R210 75-200 XR 3,340,052 9/1967 IHOVe 75 200 XR 3,350,242 10/1967 Fuchs 75 224 XR 3,389,990 6/1968 Gullett.

CARL D. QUARFORTH, Primary Examiner A. I. STEINER, Assistant Examiner US. Cl. X.R. 

